1. Field of the Invention
The present invention relates generally to catheters having an expandable balloon and to premounted balloon expandable stent balloon catheters generally. More specifically, the present invention is directed to dilatation balloon catheters having a removable protective sheath which may reduce potential trauma caused to the stent and/or the balloon during a crimping process.
2. Description of Related Art
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure which is well established for the treatment of blockages in the coronary arteries. Blockages may occur from cholesterol precipitation on the coronary wall which may be in any stage from initial deposit through aged lesions. Coronary arteries may also become blocked due to formation of thrombus.
The most widely used form of percutaneous coronary angioplasty makes use of a dilatation balloon catheter. In typical PTCA procedures, the cardiovascular system of a patient is accessed with an introducer, usually in the groin area. All other devices including a guiding catheter are percutaneously introduced into the cardiovascular system of a patient through the introducer and advanced through a vessel until the distal end thereof is at a desired location in the vasculature. A guide wire and a dilatation catheter having a balloon on the distal end thereof are introduced through the guiding catheter with the guide wire sliding through the dilatation catheter. The guide wire is first advanced out of the guiding catheter into the patient's coronary vasculature and the dilatation catheter is advanced over the previously advanced guide wire until the dilatation balloon is properly positioned across the lesion. Once in position across the lesion, the flexible, expandable, preformed balloon is inflated to a predetermined size with a fluid at relatively high pressures, such as greater than about four atmospheres, to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter may be withdrawn from the patients vasculature and blood flow resumed through the dilated artery.
In angioplasty procedures of the kind described above, there may be restenosis of the artery, which either necessitates another angioplasty procedure, a surgical by-pass operation, or some method of repairing or strengthening the area. To reduce restenosis and strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, called a stent, inside the artery at the lesion. In general, stents are prosthetic devices which can be positioned within a body cavity, for example, a blood vessel of the body of a living human or in some other difficulty accessible place. A stent generally has a diameter which may be increased or decreased. Stents are particularly useful for permanently widening a vessel which is in a narrowed state, or for internally supporting a vessel damaged by an aneurysm.
Such stents are typically introduced into the body cavity by use of a catheter. The catheter is usually of the balloon catheter type in which the balloon is utilized to expand the stent, which is positioned over the balloon, to place it in a selected location in the body cavity. The stent is expanded to a larger diameter for placement in the vasculature, often by the balloon portion of the catheter. Stents delivered to a restricted coronary artery, expanded to a larger diameter by a balloon catheter, and left in place in the artery at the site of a dilated lesion are shown in U.S. Pat. No. 4,740,207 to Kreamer and U.S. Pat. No. 5,007,926 to Derbyshire.
In advancing an inflation expandable balloon through a body vessel to the deployment site, the stent must be able to securely maintain its axial position on the delivery catheter, without trans-locating proximally or distally, and especially without becoming separated from the catheter. Stents that are not properly secured or retained to the catheter may slip and either be lost or be deployed in the wrong location or partially deployed. In securing a stent to a catheter, however, the stent must be crimped in such a way as to minimize or prevent altogether distortion of the stent and to thereby prevent abrasion and/or reduce trauma of the vessel walls.
In the past, crimping and balloon reduction has been done by hand often resulting in the application of undesired uneven forces to the stent. Such a stent must either be discarded or re-crimped. Stents which have been crimped multiple times can suffer from fatigue and may be scored or otherwise marked which can cause thrombosis. A poorly crimped stent can also damage the underlying balloon.
Recently, stent crimping devices have been disclosed in U.S. Pat. No. 5,546,646 to Williams et al, U.S. Pat. No. 5,183,085 to Timmermans et al., U.S. Pat. No. 5,626,604 to Cottone, Jr., U.S. Pat. No. 5,725,519, to Penner et al., U.S. Pat. No. 5,810,873 to Morales, WO 97/20593, WO 98/19633 and copending U.S. app. Ser. No. 09/404986, filed Sep. 22, 1999 to Klisch et al, the entire contents of each reference being respectively incorporated herein by reference.
One important characteristic of a dilatation balloon catheter as well as a stent delivery catheter is its “profile”, which is determined by the outer diameter (O.D.) of the distal end portion of the balloon and stent when deflated. The outer diameter affects the ease and ability of the dilatation catheter to pass through a guide catheter, through the coronary arteries, and across a lesion. Considerable effort has been made in developing low profile dilatation balloon catheters. U.S. Pat. No. 5,342,307, incorporated herein by reference, discloses a balloon protector sleeve used with a tri-fold dilatation balloon catheter for angioplasty. Because reduction of profile is of significance balloon reduction often includes the use of a first profile reducing “bi-tube” as well as one or more smaller balloon protectors. Typically the bi-tube is placed about the balloon after the balloon is folded and wrapped. The bi-tube is typically removed and replaced with one or more balloon protectors suitable for retaining the balloon in the reduced configuration for shipment or storage. Such use of bi-tubes and balloon protectors are also used in prior stent crimping processes as will be described in greater detail below.
Minimization of “profile” is of importance in balloon catheters and stent delivery systems. In addition to securing the stent onto the balloon catheter, the crimping process may also provide the catheter with a reduced profile configuration. Accordingly, the balloon protector of the present invention is particularly directed for use with balloon catheters and stent delivery systems wherein the protector provides the balloon and stent with protection during the crimping process, thereby allowing the stent to be safely secured to the balloon in a reduced profile state.
All US patents, applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.